Biodegradable resins begin to degrade in several weeks by actions of enzymes produced by microorganisms living in nature in a case where the biodegradable resins are placed in soil, sea waters, or inside the body of animals, and disappear during a period of about an year to several years. Therefore, in recent years, utilization of the resins is being remarked from the viewpoint of increased interests in environmental-friendliness.
For example, Patent Publication 1 discloses that when a polyester-based plasticizer having a repeating unit of a divalent alcohol, terminals of which are capped with a monobasic acid and/or a monohydric alcohol, the polyester-based plasticizer having a total of acid value and hydroxyl value of 40 or less, is used, the polyester-based plasticizer has excellent compatibility with the polymer, whereby a resin composition having excellent water resistance and flexibility while maintaining transparency of a lactic acid-based polymer is obtained.
In Patent Publication 2, it is reported that a resin composition having excellent flexibility and storage stability is obtained by melt-kneading a lactic acid-based polyester previously subjected to deactivation treatment of a polymerization catalyst with a chelating agent and/or an acidic phosphoric ester, with a plasticizer, and that a molded article having excellent heat resistance and solvent resistance is obtained by molding and crystallizing the composition.
In Patent Publication 3, an amorphous sheet obtained by extruding a polylactic acid composition containing a polylactic acid resin, a plasticizer, and a crystal nucleating agent in a molten state is rapidly quenched to solidify a crystal nucleating agent, and thereafter an extruded mixture is heated to crystallize, whereby a polylactic acid resin sheet having excellent heat resistance and printability is obtained.
In addition, in Patent Publication 4, it is reported that when a molded article obtained by vacuum molding, pressure molding or vacuum pressure molding a resin composition prepared by blending an aliphatic polyester with a particular (poly)glycerol ester-based plasticizer has an appropriate softness, and is allowed to pierce though a hole or the like, the cutting edges are clean and cracking does not take place therefrom, and a plasticizer used is not eluted into water, so that the molded article does not cause bleed-out even at high temperatures, and has high heat resistance.
Patent Publication 5 discloses that a sheet made of a lactic acid-based polymer composition prepared by blending a lactic acid-based polymer with an organic crystal nucleating agent containing an aliphatic carboxylic acid amide having an amide bond, and a crystallization promoter, such as a phthalic acid derivative, an isophthalic acid derivative, an adipic acid derivative, a maleic acid derivative, a citric acid derivative, an itaconic acid derivative, an oleic acid derivative, a ricinoleic acid derivative, a phosphate ester, a hydroxypolycarboxylic acid ester, or a polyhydric alcohol ester, is treated to have a crystallinity of from 20 to 50%, and thereafter subjected to a secondary molding, thereby obtaining a thermoformed article having excellent heat resistance and transparency at excellent production efficiency.
In addition, in Patent Publication 6, it is reported that a composition prepared by blending an aliphatic polyester with a particular (poly)glycerol ester-based plasticizer shows inhibition of bleed-out of the plasticizer, so that the composition is suitable as raw materials for a molded article such as a film having excellent transparency, heat resistance, and flexibility. In addition, as the film, a stretched film having a crystallinity of from 20 to 60% is disclosed.
In Patent Publication 7, in a resin composition prepared by blending a composition containing a polylactic acid resin and a flame retardant with a cellulose having a crystallinity of less than 50%, an example where an oligoester-based plasticizer is further blended is disclosed. A molded article obtained by injection-molding the above resin composition shows excellent strength, flexibility, impact resistance, and flame retardant property.